Method for coating sheets



METHOD FOR COATING SHEETS Filed Ma 6, 1940 2 Sheets-Sheet l 40 30 a5 21 3 36 41 20 l9 0 o I n L .26 17 49 a: .25

INVENTQR DODB/OIAMCJ/VWUP 1 v i v /W Oct. 28, 1941. D. McARTHUR 2,260,392

METHOD FOR COATING SHEETS Filed May 6, 1940 2 Sheets-Sheet 2 43:06 5 35,5 55/ 455 45 INVENTOR Z www g 1 Patented Oct. 28,1941

METHOD FOR COATING SHEETS Donald A. McArthur, Warren, Ohio, assignor to The Wean Engineering Company, Inc., Warren, Ohio, a corporation of Ohio Application May 6, 1940, Serial No. 333,476

3 Claims. (01. 91--70.2)

This invention relates generally to the coating coating bath and, in particular to the galvanizing of ferrous sheets.

The apparatus usually used for galvanizing sheets comprises a zinc pot adapted to contain the coating bath and a galvanizing rig removably disposed therein. The rig comprises a frame having entry rolls, bottom rolls and exit rolls, with suitable guides therebetween. Numerous types of motor drive have been proposed heretofore for the several sets of rolls of a galvanizing rig but none of them, so far as I am aware, has fully satisfied the exacting requirements of this specific application.

When the speed of a motor is varied by changing the applied voltage, the horse-power output of the motor decreases directly with the speed. Such an arrangement for driving the rolls of a galvanizing machine has not been thought feasible heretofore because it has previously been the belief of those acquainted with the problem that a galvanizing machine constitutes a substantially constant-horse-power load, i. e., that the required torque is higher at low speeds than at high speeds. I have discovered, however, that the previous conception with respect to the character of the load constituted by the rolls of a galvanizing machine is an erroneous one and that a galvanizing machine is a load requiring a substantially constant torque. As a mattter of fact, experimental data which I have obtained show that the torque required at low speeds, far from being greater than that required at high speeds, is actually somewhat less than the torque required at high speeds.

A motor operating on a variable-voltage supply is not well suited for a constant-horse-power load. This is because the horse-power output of the motor decreases at low speeds, by reason of the drop in applied voltage, and the motor must, therefore, be designed for an output capacity much greater than that actually required at high speeds, in order to have the necessary torque at low speeds. Thus, at high speeds, the motor outmuch greater than that required to give the horse-power output required at high speeds, that the cost of such motors would be relatively excessive.

I am able to utilize standard motors connected to a variable-voltage source for driving galvanizing-machine rolls because, even though the horse-power output of the motors decreases when they are-slowed down by decreasing the applied voltage, the torque remains substantially the same, the decrease in horse-power being proportionate to the decrease in speed. The torque. exerted by the motors at high speeds is ample for driving the rolls at low speeds. The motors therefore deliver substantially their rated output when operating at high speeds, and no excess capacity is required to provide the necessary torque at low speeds.

The several sets of rolls of a galvanizing rig -must be so driven that their peripheral speeds are the same. Any difference between the peripheral speeds of successive sets of rolls creates buckling and distortion of the sheets or causes them to be scratched by the guides. The problem of accurately'equalizing the peripheral speeds of the several sets of rolls is further complicated by the fact that these rolls must be frequently re-dressed in order to maintain the surface thereof smooth. This necessarily involves a-slight reduction'in their diameter, making it necessary to drive them at a somewhat higher angular speed in order to maintain the same peripheral speed. This re-dressing of the rolls is sometimes necessary as frequently as once every eight hours. A further factor is the building up of accumulations ofinaterial on the rolls which also changes their effective diameter.

Numerous attempts have been made heretofore to equalize the peripheral speeds of galvanizing machine rolls accurately. Change-speed gears have been used but they are subject to serious disadvantages. Only certain predetermined speed ratios are available and the setting'of the changespeed gear cannot readily be altered while the machine is running. Variable-speed drives of different types have also been employed but have not been entirely satisfactory because their rather complex construction requires considerable maintenance in view of the necessity of locating the drive near the galvanizing pct.

In the galvanizing of sheets by conventional galvanizing machines, furthermore, the formation of cobbles is a serious problem. If a sheet cobblesafter passing through the flux rolls, the entiremachine must be stopped in order to avoid damage which would result from feeding a following sheet in on top of the cobbled sheet. This f rolls very accurately and thereby and scratching.

spoils the preceding sheet gripped by the bottom and exit rolls and already part way out of the bath.- The machine must also .be stopped, of course, when a sheet cobbles between the bottom and exit rolls. In either case, the removal of. the

cobbled sheets is difiicult and the temporary shutdown necessitated thereby reduces the output.

My novel method and apparatus for coating sheets fully overcome the aforementioned objections .to galvanizing machines as now constructed. In a preferred embodiment of the invention, I provide an independent drive for each of the sets of rolls of a galvanizing machine and means for stopping and reversing each set independently of the others. In aspecific embodiment of the invention, I provide a separate motor for driving each of the sets of rolls, 1. e., entry rolls, bottom rolls, and exit rolls, through suitable speed reducers, and supply energy to all the motors from a common source, the voltage of which may be varied at will, to vary the speeds of all the motors simultaneously. In addition, each motor has its own individual speedcontrol means, as well as the means for stopping it and reversing it independently of the other motors. One advantage of this arrangement is that if a sheet cobbles between the entry and bottom rolls, while the preceding sheet is still engaged by the exit rolls, I am able to stop the entry and bottom rolls while continuing to oper- 1 ate the exit rolls to deliver the sheet gripped thereby without spoiling it. I am also able to 1 reverse any of the sets of rolls individually to i remove, the cobble and actually pull out any buckling of the sheet which may have occurred.

vIn the typical case above-mentioned, the flux rolls are reversed while the bottom rolls remain stationary, until the cobble is removed and any buckle formed thereby is pulled out. 1 The invention also makes it possible to equalize the peripheral speeds of the several sets of.

avoid buckling A preferred embodiment of the invention is illustrated somewhat diagrammatically in the accompanying drawings and the method will be explained by reference thereto. In the drawings,

1' elevation;

1 drive embodying my invention;

Fig. 1 is a partial plan view of a galvanizing line showing the galvanizing machine proper and a portion of the spangle conveyor;

Fig. 2 is a longitudinal section along the plane of the line 11-11 of Fig. 1, parts being shownin Fig. 3 is a plan view of a galvanizing-machin Fig. 4 is a section taken along the line IV-IV of Fig. 3 with the galvanizing rig removed from the pot and showing the drive therefor in side elevation; and i Fig. 5 is a diagram illustrating the connection so of the motors to their variable-voltage supply and- 1 the individual control devices for each motor.

Referring now in detail to the drawings and for the pot to maintain a bath of zinc contained therein, in molten condition. A galvanizing rig indicated generally at I2 is removably disposed the pot I0 and comprises a frame l3 having 7 entry rolls l4, bottom rolls l5 and exit rolls l6 journaled therein. Between adjacent pairs of rolls, guides l1 and I8 are located so that when the rolls are driven, sheets entering the pot successively traverse a well-defined path there-Q through.

Cooperating with the entry rolls l4 areguides l9 adapted to receive sheets emerging from a flux bath (not shown) and direct them between the entry rolls. A spangle conveyor 20 receives the sheets as they are discharged successively from the bath by the exit rolls 1 6.

The drive for the rolls of the galvanizing m achine or rig is indicated generally at 2| and will be described in detail with particular reference to Figs. 3 and 4. 'An adjustable base plate 22 is movable along guides 23 in a sub-base 24. A screw shaft 25 journaled in a thrust bearing 26 secured to the sub-base 24, is threaded through a nut 21 received in a socket in the base plate 22. Clamping bolts 28 extending through slots 29 formed in the base plate 22 permit it to be sedrive 34 connects the shaft 3| to one of the entry rolls I 4 which are geared together. A second chain and sprocket drive 35 connects the shaft 3| to the exit rolls of the flux bath (not shown).

A motor 36 on the base plate 22' drives a bevelpinion shaft 31 journaled in a bearing 38 on the base plate, through a speed-reducer 39 which is illustrated as of the worm-gear type. ,A bevel pinion on the shaft 31 meshes with a gear ll on a drive shaft 42 journaled on the frame H3 in a generally vertical position. A worm 43 at the lower end of the shaft 42 meshes with a worm wheel on the lower one of the bottom rolls l5 which are geared together.

A motor 45 mounted on the base plate 22 drives a shaft 46 journaled in a bearing on the base plate, through a speed reducer 48 generally similar to that shown at 39.. A pinion 49 on the shaft 46 meshes with a gear on one of the exit rolls 16, the rolls being geared together.

It will thus be apparent that each of the sets of rolls embodied in the galvanizing-machine rig is driven by a separate motor. The motors 30, 36 and 45 are adapted to be supplied with current from a variable-voltage supply bus 50. Any convenient source of current may be employed but I have illustrated a generator 5| driven by a direct-connected motor 52. The generator field 5lf is controlled by a rheostat 5lr whereby the voltage across the bus 50 may be varied. The field winding 30 of the motor 30- is controlled by a rheostat 301- and the motors and 45 have .corresponding elements similarly designated.

In order to permit each of the motors 30, 36 and 55 to be independently controlled, I provide means for stopping and reversing each motor individually. Such means for controlling motors are well-known and need not be disclosed nor described in detail. For the purpose of illustration, I have shown in Fig. 5 a manual reversing switch 30s for the' motor 30 and similar switches for the motors 36 and 35. It will be understood however, that the reversing switches are intended merely as diagrammatic symbols for complete starting and reversing panels, preferably push-button controlled.

Excitation current for the field windings of the generator 5| and the motors 30, 3B and 45 is preferably supplied by an exciter generator (not shown) which may conveniently be driven by the motor 52.

The galvanizing-machine drive and the con trol system therefor as shown in the drawings make it possible to vary the speed of all the rolls simultaneously to the same extent, as well'as to vary the speedof 'each set of rolls independently of the others. The speed of all motors may be varied simultaneously by varying the rheostat lr of the generator 5| and the speeds of the several motors may be similarly controlled independently. The individual speed-control means for the several motors may be employed to vary the speeds of the several motors similarly, after the maximum range of adjustment available by means of the rheostat 5lr has been taken advantage of. The generator 5i may readily be constructed to provide a voltage ratio of 4.5:1 or more. The motors 30, 36 and 45 may conveniently be designed for a ratio of maximum to minimum speed by means of the field rheostat, of 2:1 or more. It is thus possible to obtain an overall adjustment of the speeds of the'motors in the ratio of 9:1 or more.

It will be apparent that the apparatus described makes it possible to equalize accurately the peripheral speeds of the several sets of rolls.

out any buckle formed therein by the cobbling. As in the instance previously described, the exit though the horse-power output of the motors decreases on a drop in the voltage of the gener- 'ator 5i, this decrease is effected by a reduction in the speed of the motors without materially reducing their torque. The motors are thus loaded to approximately the same percentage of their capacity throughout the speed range ob- In operating the apparatus, if it is observed that one set of rolls tends to run ahead of or behind the others, a slight adjustment of the field rheostat of the motor driving the rolls which are not properly synchronized will efiect the desired equalization of peripheral speeds. Any lack of such equalization quickly becomes apparent from the buckling of the sheets between successive sets of rolls so that they come out with a bad shape, or from the scratches formed by the'guides if the portions of the sheets between adjacent sets of rolls are stretched too taut. The field rheostats may be constructed to provide variation of the motor speeds by very small increments so that accurate equalization may easily be obtained, re-

' being fed into the bath by the entry rolls I4 becomes cobbled, it is a simple matter to stop the motor 30, by opening'the switch 303, thus pretime, the preceding sheet engaged by the exit rolls and possibly the bottom rolls continues to travel upwardly and out of the bath for delivery to the spangle conveyor 20. This avoids spoiling the uncobbled sheet which was inevitable heretofore because of the necessity for stopping the entire machine. Once a sheet has started to emerge from the bath, any stoppage thereof before it has completely emerged leaves a mark which renders the sheet unfit for sale as prime material.

The apparatus is also capable of removing a buckle in a cobbled sheet. If a sheet becomes cobbled between the bottom rolls and the exit rolls and while it is still engaged ,by the entry rolls, the entry rolls and bottom rolls are stopped and reversed to clear the cobble. When the leading edge of the sheet has been pulled back substantially to the bite of the bottom rolls, the latter may be stopped and the reverse rotation of the entry rolls continued to stretch the sheet between the entry rolls and bottom rolls-and pull tained by varying the voltage of the generator Bl.

It will be apparent that the invention v is characterized by numerous advantages over drives for galvanizing machines as heretofore constructed. The mechanical equipment necessary to provide complete and continuous adjustability of the speeds of the rolls. is reduced to a minimum, involving only the 'field rheostats of the motors and generator. The ability to stop and reverse each set of rolls independently of the others makes itpossible to prevent the entry of a new sheet into a machine where one is already cobbled, as well as to permit the removal of the cobble itself and the continued progress of the preceding sheet through the bath and out between the exit rolls. Precise equalization of the peripheral speeds of the several sets of rolls can easily be obtained and maintained continuously, by making slight adjustments as the case demands. Since it is unnecessary, in order to obtain the desired range of speed adjustment, to design the motors for more than a 2:1 speed ratio, they are characterized by better regulation'and lower cost than if it were necessary that they be capable of a greater ratio of speed adjustment.

A further advantage resides-in the extreme simplicity of the drive from the mechanical standpoint and the consequent minimizing of maintenance as well as the reduction in vibration when the drive is operating.

Although I have illustrated and described but a preferred embodiment and practice of the invention, it .will be evident that changes in the construction and procedure disclosed may be made without departing from the spirit of the invention or the scope of the appended claims.

I claim: v

1. In a method of coating sheets by passing them successively through a galvanizing bath, between entry rolls thereabove and bottom rolls and exit rolls immersed therein, the steps in-- cluding driving all said rolls at substantially the same peripheral speed, and upon the cobbling of a sheet between the entry and bottom rolls,

stopping the entry rolls thereby preventing the entry of another sheet, while continuing todrive the bottom and exit rolls thereby discharging the preceding sheet without spoiling it.

- 2. In amethod, of coating sheets by passing them successively through a galvanizing bath, 1

' eluding driving all said rolls at substantially the same peripheral speed, and upon the cobbling then again driving all the rolls in such direction 10 as to feed the sheet forward through the machine.

3. In a method of coating sheets by passing them successively through a galvanizing bath between entry rolls thereabove, and bottom rolls and exit rolls immersed therein, the steps including driving all said rolls at substantially the same peripheral speed, stopping the entry rolls only upon the occurrence of a cobble between them and the bottom rolls, and reversing the entry rolls to pull out the cobbled sheet, while continuing to drive the bottom and exit rolls to discharge the preceding sheet without spoiling it.

DONALD A. McARTHUR. 

